1 Samuel 27:1
And David said in his heart, I shall now perish one day by the hand of Saul: there is nothing better for me than that I should speedily escape into the land of the Philistines; and Saul shall despair of me, to seek me any more in any coast of Israel: so shall I escape out of his hand.
The verse belongs to the account of David's flight from Saul after Abiathar escaped Saul's slaughter of the priests and joined David. Though David knew God had chosen him to rule Israel and had opportunities to kill Saul, he would not harm the king God had anointed. The verse records his decision to escape Saul's pursuit and hunting by seeking refuge and safety in the land of the Philistines.
The move came after his trust in God failed and when he acted without seeking God's counsel. At Gath he felt secure from betrayal and settled with his family, household, possessions, and men, apparently intending to remain there. Achish welcomed him partly from admiration and partly hoping his example would draw other Hebrews to his side, and he promised to protect the Israelite fugitives.
The protection David accepted came from people whose favor was driven by self-interest, hoping to separate his forces from Saul's army and have him fight against Saul and Israel. By acting prudently and humbly, he made even his enemies peaceful toward him. He remained among the Philistines until Saul's death.